Liberal Senators are "holding their breath," worried that President Barack Obama will capitulate to Republican demands for a large spending-cuts-only package in the final push to avoid a debt default by the Tuesday deadline.

A press conference Saturday afternoon where Speaker John Boehner (R-Ohio) and Senate Minority Leader Mitch McConnell (R-Ky.) expressed optimism that they would soon reach a deal with the White House had liberals nervous, Sen. Tom Harkin (D-Iowa) said.

"A lot of us who are progressives are very concerned about how far the president might go," Harkin said. "I'm very concerned about that, yes I am. And we're ... holding our breath."

Harkin said he was happy when Senate Majority Leader Harry Reid (D-Nev.) dismissed McConnell's confidence that Republican leaders could soon reach a deal with the White House.

Instead of cutting a bad deal and capitulating to Republicans, Harkin said, the president "must" exercise his authority to avoid a financial calamity. Harkin said Obama has the responsibility to uphold the payment of the country's obligations.

Harkin said there are precedents for such extraordinary action that is not explicitly spelled out in the Constitution — pointing to the Louisiana Purchase by President Thomas Jefferson and the Emancipation Proclamation by President Abraham Lincoln.

And Harkin pointed to a justice opinion in Perry v. the United States that he said cites the 14th Amendment to argue that Congress does not have the power to prohibit the payment of the country's obligations.

Harkin's view is shared by many Democrats in both chambers, who feel that they have already compromised too much with House Republicans.

Sen. Bernie Sanders (I-Vt.) also cited the 14th Amendment clause that says the debts of the United States "shall not be questioned."

"I think that is just what he should do," he said.

Sanders said giving in to Republican demands for deep budget cuts under the threat of not paying the nation's bills would set a "horrendous precedent."

Republicans, however, left a quorum call vote optimistic that a deal would get done soon.

Several Republicans said they were told by McConnell that both sides are moving closer together in the negotiations with the White House, although they declined to detail specifics.

"There is a lot of progress being made, a lot of progress," Sen. Bob Corker said. "I think they will have a deal soon and then need to come back and talk to Members about it. ... Maybe there's some angst about that on the other side."

The Tennesse Republican dismissed the various talks going on among Senators about alternatives to the deal, and said in the end only about four or five people matter. "I guess it's nice for people to do, but it's not relevant anyway to getting a deal done," Corker said.

Meanwhile, Senate Minority Whip Jon Kyl (R-Ariz.) said the final deal should build off of the Boehner bill after the Reid bill is defeated Saturday night. That saves a cloture vote, Kyl noted, because it is a House measure, and having Boehner's name on the legislation won't hurt getting the bill through the House.